Both environmental and economic concerns in recent years have driven a move toward conserving energy in building utilities such as lighting and heating, ventilation and air conditioning (HVAC). Various methods have been used in the past to conserve energy in these service utility areas and have been met with limited success. For example, ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers) ventilation standards now provide algorithms for adjusting ventilation rates based on occupancy in order to reduce energy consumption when demand falls below default levels. Systems have been developed that estimate occupancy based on levels of carbon dioxide measured in the ventilated space. But these carbon dioxide based systems have several disadvantages, including the reliability and accuracy of the carbon dioxide monitors and the costs associated with installing and maintaining them.
In addition, some systems use radio frequency identification (RFID) tags to monitor occupancy of a zone and others use active RFID tags to set different parameters of an HVAC system directly, in accordance with the needs of the person or product to which the tag is attached. But none of the systems has the capability of automatically and immediately adjusting light intensity and/or ventilation rates based on accurate occupancy levels.
The patent issued to Stortoni, U.S. Pat. No. 7,545,267, discloses a system in which RFID tags attached to climate-sensitive products signal a transponder in the storage area, which transponder signals one or more building control systems (such as HVAC) to adjust to the product's optimal environment. This system is not designed to address occupancy-based demand-controlled ventilation (DCV) and is not adaptable to that purpose. The Stortoni system requires expensive and bulky active RFID tags having substantial internal data content which serve no purpose in the DCV context.
The patent of Carrender, U.S. Pat. No. 6,927,687, discloses an apparatus that uses RFID tags and readers to monitor environmental conditions in a given area. The functions of this apparatus are unrelated to determining occupancy and/or controlling area ventilation rates.
The patent to Gazdzinski, U.S. Pat. No. 6,988,071, describes a “smart elevator” system that keeps track of occupancy levels in elevator car and/or destination floors by detecting RFID tags carried by passengers. While there is an embodiment of this system that involves control of HVAC in areas of the destination floor, this control is exercised by the elevator passenger manually activating a key pad or touch screen within the elevator. Therefore, the function of automatically setting ventilation levels in areas based on RFID-detected occupancy is not addressed.
The patent application of Agrawal, et al., US 2008/0048826, involves a system that uses an RFID badge to track an occupant's movement through an area and automatically disable certain hazards in the occupant's path for safety purposes. No means of counting occupants in the area or using that data to control ventilation rates is disclosed.
The patent issued to Myllymaki, U.S. Pat. No. 6,348,867, is a system that automates building control systems in accordance with an occupant's physiological condition as monitored by a wrist-held sensor. Occupancy-based DCV is not an object of this invention.
The patent of Funakoshi, et al., U.S. Pat. No. 5,156,203, discloses an air conditioning system that adjusts itself in response to preferred settings recorded on a “smart” ID card carried by the occupant. While automatic HVAC control is featured, it is not demand-controlled based on an occupancy count.
Using alternative sensing technologies—passive infrared (PR), acoustic (micro-phonics) or ultrasonic (Doppler microwave)—means occupants must keep moving or generating sound in order to be detected. Importantly, these types of sensors call for a delay in shutting off lights after no motion or sound is detected, in case occupants are still present. It becomes a nuisance if occupants are still present and the lights go off, and the delay itself, typically 20 minutes, causes unnecessary energy consumption if the space is indeed vacant. Reducing shut off delay from 20 minutes to ten or five minutes represents significant energy savings. In an attempt to compensate for the disadvantages of dependency on sound or movement, manufacturers are now combining technologies in their platforms such as PIR/Acoustic. Known as Passive Dual Technology, PDT, dual sensors carry added cost. When lights turn off, due to lack of motion or sound, occupants that are still present must move or make sounds to turn the lights back on. Such off/on energy consumption is expensive and can shorten the life of bulbs and switches.